Ca 2+ currents in central insect neurons: Electrophysiological and
pharmacological properties.
Wicher, Dieter and Heinz Penzlin.
S[umlaut]achsische Akademie der Wissenschaften zu Leipzig, Forschungsgruppe
"Neurohormonale Wirkungsmechanismen", Erbertstra[beta]e 1, D-07743 Jena,
Germany.APStracts 3:0192N, 1996.
ABSTRACT
Ca 2+ currents in dorsal unpaired median (DUM) neurons isolated from the fifth
abdominal ganglion of the cockroach Periplaneta americana were investigated
with the whole-cell patch-clamp technique. On the basis of kinetic and
pharmacological properties two different Ca 2+ currents were separated in
these cells: mid/low voltage-activated (M-LVA) currents and high voltage-
activated (HVA) currents. M-LVA currents had an activation threshold of -50 mV
and reached maximal peak values at -10 mV. They were sensitive to depolarized
holding potentials and decayed very rapidly. The decay was largely Ca 2+ -
dependent. M-LVA currents were effectively blocked by Cd 2+ (IC 50 = 9 [mu]M),
but they had also a remarkable sensitivity to Ni 2+ (IC 50 = 19 [mu]M). M-LVA
currents were insensitive to vertebrate LVA channel blockers like flunarizine
and amiloride. The currents were, however, potently blocked by w-conotoxin
MVIIC (1 [mu]M) and w-agatoxin IVA (50 nM). The blocking effects of w-toxins
developed fast ( t on = 15 s) and were fully reversible after washing.
HVA currents activated positive to -30 mV and showed maximal peak currents at
+10 mV. They were resistant to depolarized holding potentials up to -50 mV and
decayed less pronounced than M-LVA currents. HVA currents were potently
blocked by Cd 2+ (IC 50 = 5 [mu]M) but less affected by Ni 2+ (IC 50 = 40
[mu]M). These currents were reduced by phenylalkylamines like verapamil (10
[mu]M) and benzothiazepines like diltiazem (10 [mu]M), but they were
insensitive to dihydropyridines like nifedipine (10 [mu]M) and BAY K 8644 (10
[mu]M). Furthermore, HVA currents were sensitive to w-conotoxin GVIA (1
[mu]M). The toxin-induced reduction of currents appeared slowly ( t on 120 s)
and the recovery after wash was incomplete in most cases. The dihydropyridine-
insensitivity of the phenylalkylamine-sensitive HVA currents is a property
which the cockroach DUM cells share with other invertebrate neurons. Compared
with Ca 2+ currents in vertebrates, the DUM neuron currents differ
considerably from the presently known types. Although there are some
similarities concerning kinetics, especially the pharmacological profile of
the cockroach Ca 2+ currents is very different from profiles already described
for vertebrate currents.

Received 2 July 1996; accepted in final form 4 September 1996.
APS Manuscript Number J514-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996